(1) Field of the Invention
This invention relates to electromagnetic field absorbing devices and, more particularly, to electromagnetic field absorbing devices molded of conductive loaded resin-based materials comprising micron conductive powders, micron conductive fibers, or a combination thereof, homogenized within a base resin when molded. This manufacturing process yields a conductive part or material usable within the EMF or electronic spectrum(s)
(2) Description of the Prior Art
Electromagnetic interference (EMI) is a significant issue in electronic circuits and systems. Electromagnetic energy is present at all times. For example, energy from the sun is transmitted to the earth by electromagnetic energy. Further, wireless communications systems rely on electromagnetic waves to carry voice/data/video information over long distances without the benefit of direct wire connection. While electromagnetic energy is beneficial in a variety of ways, at least two problems are relevant to the art of electronic circuits and systems.
First, electronic circuits and/or systems can radiate substantial electromagnetic energy whether intentionally, as in the case of a broadcasting wireless device such as a mobile phone, or unintentionally, as in the case of a digital microprocessor operating at a very high frequency. In either case, rapid and periodic changes in current flow direction result in radiation of electromagnetic energy from the circuit device. This electromagnetic interference (EMI) may be in a broad band or a narrow band of frequencies. The emission of substantial electromagnetic energy from the circuit device may cause no direct difficulties with the operation of that circuit device but may create a local operating environment with excessive levels of electromagnetic energy. Second, electronic circuits and/or systems may be overly sensitive to EMI present in the operating environment. That is, environmental levels of electromagnetic energy may cause faulty operation of the circuit. For example, an automobile has a microprocessor-based system to control fuel and ignition for the vehicle engine. In addition, the automobile has a radio receiver. It is found in the art that the radio receiver may exhibit poor tuning and/or sound quality due to EMI or radio frequency interference (RFI) radiating from the engine control circuit. In this case, the engine control system may be radiating excessive EMI, or the radio receiver may be overly susceptible to EMI in a particular frequency range, or a combination of these effects may be occurring. An important object of the present invention is to provide a means to reduce EMI/RFI radiation from electronic circuits and systems. A second important object of the present invention is to provide a means to reduce EMI/RFI susceptibility of electronic circuits and systems.
Several prior art inventions relate to electromagnetic interference materials and methods. U.S. patent application Ser. No. 2002/0162672 A1 to Cook et al teaches the use of a doped synthetic polymer material for packaging of power electric assemblies. This invention uses such materials as nickel, carbon fiber or aluminum in a polymer matrix. This invention also teaches the use of a doped synthetic polymer material for heat dissipation. U.S. Pat. No. 5,338,617 to Workinger et al teaches a method of insulating metal powder particles that is suitable for incorporation into plastic resins for subsequent casting to form radio frequency shields having high DC resistance. This also teaches the combining of the metal powder with thermosetting or thermoplastic materials including olefins, flouroplastics, polyamides, polyesters, silicone rubber, urethane, acrylics and/or polycarbonates to provide a conductively loaded plastic material. In particular, carbonyl iron (Fe(CO)5) is used as the metal powder. U.S. patent application U.S. Ser. No. 2002/0160193 A1 to Hajmrly et al teaches the use of conductive fillers and conductive polymers in forming EMF shielding. The conductive fillers used in this invention comprise a noble metal coating formed over a non-noble metal coating formed over a carbon-based core. In addition, copper or nickel powders used as conductive fillers are described in the prior art discussion.